Water pump on onan 6.5 gas genny

[labrador]

I took off my water pump to install a new impeller and after cussing onan for the location gave it to the yard to reinstall due to my scraped and bleeding knuckles. The mechanic went thru 4 impellers and still can't get any water flow. The seacock is open and water can be sucked thru the inlet to prime.Still nothing! The backing plate on the pump was replaced because it was scored. Anyone have any ideas!

 

[MikeP]

Was water flowing OK before it was disassembled?

Make sure the woodruff key is in place on the impellor shaft (is the impellor turning?)

Be sure to lubricate the impellor and the interior of the pump body before installing the impellor.

Make sure the gasket/O-ring is present and in good condition.

Check for obstructions in the pump inlet/outlet and beyond the pump. Remove the hose from the pump outlet and start the engine. Water should blast from the pump. If so, the obstruction is further along in the plumbing. Don't run the engine very long in this configuration since there will be no cooling provided but it won't take longer than 4-5 seconds to see if the pump is working or not.

Try the old (scored) pump cover. If it works, surface-grind it with wet sand-paper on a thick sheet of glass. You can almost always do this and restore the plate to like-new without buying a new one.

Can't think of anything else to check at the moment

Oh yeah...fire the mechanic.

 

[labrador]

Yes water was flowing before the (mechanic) got hold of it. The impeller was definatly in need of replacement. I like your idea of firing the guy. Guess I'll go get another box of band-aids and do it myself.

 

[Nonchalant1]

Mike's thoughts cover the usual stuff. When you check the outlet pressure of the pump, it's frequently easier to take the outlet hose and disconnect it at the other end, leaving it connected to the pump so you can direct the water into a bucket. If no water, then check that hose by taking it off. If it pumps water, go lok further down for impeller vanes, etc. stuck in the heat exchanger inlets, etc. I found 3 very old vanes in my pump outlet pipe elbows, even though the impeller I first took off had all it's vanes. Go figure.

Also check some "how could he do that?" stuff:
Check the cam and the screw that holds the cam in place. It's possible to spin a cam. It's also possible to forget to put it back in place so it won't pump at all.
Check the inlet and outlet hoses for being reversed. That should be almost impossible on most setups, but who knows.

Good luck,

Doug Shuman

 

[dwaynec]

Mike,
What grit sanpaper is fine enough? I am getting ready to change my impellors this weekend and if I have to do a little cleanup, I might as well have the supplies on hand vs another time consuming trip to the store.
Thanks,
Dwayne

 

[MikeP]

220 wetordry will probably be sufficient, followed by a few passes with 400. If the scoring is pretty deep you could start with something coarser but finish with the 400. You will need several sheets of the 220 (or whatever grit you start with) for each plate. One sheet of 400 for each will be plenty. Work the plate in a figure 8 motion. Keep the paper wet with soapy water and flush frequently.

 

[labrador]

Spoke with the yard today and they said it worked when they poured water in the line to prime. Checked it several times after that and it worked fine. Then they gathered tools an smoked a few (in the engine room as I found their butts ground out on the battery box) and checked it again. NO GOOD. I'm going to put a check valve down by the seacock to see if that will keep it primed as a new waterpump for this old mostrosity is about 650.00. If that doesn't work I'm thinking of putting in a 12v air conditioning pump which will come on when the gen starts. Any comments?

 

[Maynard Rupp]

It has to work. It has no options. We have one and I changed the impeller last year. The old one was worn and hard but still pumped. I took the pump off and changed it, put the pump on, and it worked fine. There is no magic. If the cover plate and gasket don't leak, and the impeller turns, It has to pump water. If the outlet hose is plugged, unplug it. Remove the outlet hose and look inside with a flashlight while you rotate the pump. Does the impeller turn? Dis you buy the correct impeller? Is the rear cover plate sealing well?. If all that is true and water is available from the inlet hose, you will get soaked while you look into the outlet port when the pump is turning.

 

[captddis]

If the seal is sucking air It will not prime. The pump can easily be rebuilt if needed no need to buy a new one. Dave

 

[jim rosenthal]

No offense, but I would not reengineer this just because the yard guys haven't figured it out. It worked before; it should work again. They are overlooking something or installing it wrong. If there isn't an air leak, it will prime and pump- IF the impeller is turning.
By the way, you may be able to get the pump a lot cheaper by trying Oberdorfer pump company. I think they are in PA. Years ago I had a similar problem and got a pump from them which they sell to Onan. Good luck.

 

[labrador]

Okay guys you're not going to believe this(or maybe you will). I took off the pump Fri night and it had a blue hard rubber impeller with a hard plastic center pressed into it that slides onto the shaft and keyway. With the hard rubber, the vanes on the impeller must be facing the correct way as they are too stiff to self right themselves when turning the wrong way. You got it,the (mechanic) installed 6, yes I said 6, impellers into the pump backwards! When power was applied the plastic housing on the keyway cracked allowing the shaft to freewheel. Sat. morning I went and got a soft rubber impeller from an onan dist. with a brass insert that slids over the keyway, installed it, fired it up and would you believe it, IT WORKS FINE. First time every time. No check valve for prime. No problems at all. The yard is closed today however I'm taking the old impeller over there tomorrow to show the owner of the yard the old impeller and discuss the fact that a dummy like me can fix what his "certified mechanic" took at least 4 hours and 6 impellers to not only not fix but tell me there has to be something wrong with the pump and suggest corrective action which was not warranted. Guess from now on I'll just stock up on the band aids and try to do everything myself. Thanks for all the suggestions.
Skip

 

[MikeP]

Another addition to an unfortunately huge body of evidence which verifes that if you want something done right - do it yourself. If you really can't do it yourself, read the service manual and stand over whoever IS doing it!

 

[Nonchalant1]

Welcome to the Skinned Knuckles Club!
You already have the right type of thinking to do it yourself. Now you have the intention to do it too. Your boat will benefit from it.

Doug

 

[Maynard Rupp]

See, I told you that it has to work. I have been an aircraft mechanic all my life and all you have to do to succeed is be logical. There is NO MAGIC. Anyone can do any of this stuff. You may need to swear and use bandaids, but you can do it.

 

[labrador]

Well you got the swearing and band aids right! My gripe is that these mechanics get paid good money, and if they can't fix simple problems what do they do when something complicated comes along. I agree that from now on the manual comes out and I try to fix it with a little help from my friends, Y'all know who you are now don't ya. Thanks again for the help.
Skip

 

[MikeP]

Mechanics

It's important to understand and accept the fact that most of these guys are, to put it bluntly, incompetent. Additionally, some are maliciously so and will intentionally lie and otherwise distort the situation to work in their favor. I have heard some unbelievable cr@p come out of the mouths of marina mechanics.

Last year the marina mechanic convinced the guy in the slip next to me that he needed a new $7000 genny. Turned out what he needed was a new $5 fuel filter.

So do it yourself!

As Maynard said, none of this is magic.